[ns] Getting the same trace file over and over?

[AIG]

Hi,

I have very simple scenario, 5 nodes sending CBR traffic to a sink (I am
only looikng at MAC layer). Every time I run the tcl file, I get the exact
same trace file. However, this should not be the case since 802.11 chooses
random backoff value, and, therefore, the trace should be differnt at every
run. Does anyone have an idea what I am doing wrong?

Thanks.